1. Field of the Invention
The present invention relates generally to wheelchairs, and more particularly to an improved hand rim assembly for a hand-propelled wheelchair.
2. Description of the Background Art
The majority of hand-propelled wheelchairs in present use are equipped with a single tubular aluminum hand rim mounted offset from and towards the outside of each of two major wheels. Users generally maneuver these hand-propelled wheelchairs by gripping the hand rims and applying an appropriate torque. The torque applied to the hand rims by the user is then transmitted to the wheels via a rigid connection, thus resulting in rotational movement of the wheel and translational movement of the wheelchair. Once the wheelchair is in motion, the user may turn and brake the wheelchair by applying an appropriate level of grip force to the hand rim while maintaining a generally fixed arm position.
The single hand rim is typically rigidly attached to the wheelchair wheel using rigid machine screw fasteners between the wheel and the hand rim. Hand rim diameters are normally proportional to the size of wheel onto which the hand rim is mounted. Moreover, conventional hand rims commonly have a tubing diameter of about 0.75 inches. While generally suitable for propelling and maneuvering the wheelchair, conventional hand rims have some inherent disadvantages.
For example, the relatively small tubing diameter of a single hand rim provides a very small gripping surface for the user. As such, the pressure against the user's hands on the hand rims is relatively high as the user pushes down on the hand rim with sufficient force to propel or otherwise maneuver the wheelchair. For many users, this level of pressure against the hands may be uncomfortable or even painful.
The frictional characteristics of the surface coating of the single hand rim are limited by the need to avoid burning of the skin during braking and turning as well as the need to not abrade the user's hands. Conventional hand rims are normally formed of metallic materials, which typically have relatively high heat transfer characteristics, which tend to prevent the palms of the hands from being burned during braking. Such hand rims also tend to have relatively smooth exterior surfaces to prevent the user's hand from being abraded during braking and maneuvering by gripping the rim, which may or may not be rotating. Unfortunately, however, these smooth-surface metallic hand rims have low frictional characteristics. In order to compensate for the limited friction, users must apply a large grip force to facilitate propulsion, braking, or turning. For many wheelchair users, however, the application of a large grip force is uncomfortable, difficult, or functionally impossible.
The rigid connection between the hand rim and the wheel also tend to cause repetitive shock loading of the arms and hands of the user during propulsion. That is, as wheelchair users repeatedly push and release the hand rims, the associated repetitive loads on the hands, wrists, elbows, and shoulders can be significant. Indeed, the incidence of cumulative traumatic disorders, such as carpal tunnel syndrome and impingement syndrome of the shoulder, are currently estimated by some to be between about 30% to 50% of hand-propelled wheelchair users. These injuries may lead to a loss in the functional independence of many wheelchair users.
One proposed hand rim design, disclosed in U.S. Pat. No. 4,366,964, provides a single rim with an expanded grip surface. This enlarged single hand rim design, however, does not address the frictional disadvantages nor the reduction of repetitive shock loading during propulsion.
It is therefore the object of the present invention to provide an improved hand rim apparatus for use on hand-propelled wheelchairs, which effectively addresses the limitations of the currently available technology.